Thomas An English Engineer Colby, born at Rochester, Sept. 1 1784, died in Liverpool, Oct. 9, 1852. He was educated at the royal military academy at Woolwich, and received his first commission as second lieutenant of engineers when 17 years old. The next year he became chief personal assistant of Captain Mudge, then superintendent of the ordnance survey. During the four following years he passed the summers in making observations at various prominent points, and the winters in preparing the results for publication and superintending the engraving of the ordnance maps. He became identified with the great trigonometrical survey of England, and upon the publication of the third volume of the records his name appeared associated with that of Col. Mudge upon the title page. In 1807 he was raised to the rank of captain. In 1813 it was determined to extend the meridian line into Scotland, and Capt. Colby was placed in charge of the work. In 1817 he accompanied Biot, a scientific agent of the French government, on his trip to Shetland, and afterward assisted in connecting the French with the English tri-angulation by observations across the straits of Dover. Upon the death of Gen. Mudge in 1820, Colby was appointed his successor as superintendent of the survey and in the board of longitude, was elected a fellow of the royal society, and promoted to the rank of major, and soon after to that of lieutenant colonel.

Having undertaken a thorough survey of Ireland, he received the sanction of the duke of Wellington for raising and training three companies of sappers and miners to aid in the work. After a series of experiments on the heating and cooling of metallic rods, he succeeded in so uniting a bar of brass and iron that its extremities always remained the same distance apart whatever the temperature. With this "compensation bar" he measured a base line of eight miles on the south side of Lough Foyle; and such was the exactitude obtained that the same apparatus has since been used in the re-measurement of the English bases, in measuring a base at the Cape of Good Hope, and also those required for the great arc of the meridian in India. Col. Colby continued his superintendence of the survey till his promotion in 1846 to the grade of major general, when by the regulations of the service his active connection with it ended. He had brought English maps to an excellence not before attained, marking the seconds of latitude and longitude on the margin, and introducing into them geological facts and features.